The present invention relates to an apparatus and method for inspecting a ball bearing, with a pre-load being applied to the ball bearing to be inspected in the axial direction thereof, physical quantities such as vibrations, sound pressures and the like which are generated from the ball bearing to be inspected due to the relative rotation between the inner and outer rings of the ball bearing are measured, and the ball bearing is inspected based on the results of such measurement.
Generally, a ball bearing consists mainly of an inner ring which includes a groove, as a raceway, formed on its outer peripheral surface and is to be fixed to the rotary shaft of a rotatable mechanical part, an outer ring which includes a groove, as a raceway, formed on its inner peripheral surface and is to be fixed to a bearing portion, and a plurality of steel balls or balls formed of ceramics or the like (description will be given hereinafter of the steel balls as the representative thereof) which are inserted between the respective grooves of the inner and outer rings. After the ball bearing is assembled, the ball bearing is usually delivered to an inspection process in which the ball bearing is synthetically inspected for the quality thereof. In this inspection process, the ball bearing is inspected according to a method in which the inner ring of a ball bearing to be inspected is mounted on a reference rotary shaft rotatable on its own axis, with a pre-load being applied to the outer ring of the ball bearing to be inspected in the axial direction thereof, the reference rotary shaft is rotated to thereby rotate the inner ring relative to the outer ring, physical quantities such as vibrations, sound pressures and the like which are generated from the ball bearing to be inspected due to the relative rotation between the inner and outer rings are measured, and the ball bearing is inspected for the quality thereof on the basis of the results of such measurement.
Next, description will be given below in detail of the above-mentioned inspection method and a ball bearing inspection unit used to enforce the inspection method with reference to FIGS. 1 and 2. Here, FIG. 1 is a structure view of the main portions of a conventional ball bearing inspection unit, and FIG. 2 is a typical view of a ball bearing which is inspected by the inspection unit shown in FIG. 1, showing how each of the steel balls of the ball bearing rolled around its own axis and revolves around the reference rotary shaft.
A conventional ball bearing inspection unit, as shown in FIG. 1, comprises a bed 50 on which there are carried bearing rotating member 60 used to rotate the inner ring 4b of a ball bearing 4 to be inspected, and pre-load applying member 70 for applying a pre-load to the outer ring 4a of the ball bearing 4 to be inspected.
As shown in FIG. 1, the bearing rotating member 60 comprises a spindle 30, while the spindle 30 includes a spindle rotary shaft 1 which is supported by a plurality of radial bearings 31 and a plurality of thrust bearings 32 (which are both air hydrostatic bearings). The spindle rotary shaft 1 includes one end 1a which is structured such that the inner ring 4b of the ball bearing 4 to be inspected can be mounted on it, while a pulley 36 is mounted on the other end 1b of the spindle rotary shaft 1. The spindle rotary shaft 1 can be rotated by a drive force given by a rotation drive motor 34, while the drive force of the rotation drive motor 34 is transmitted to the spindle rotary shaft 1 through a pulley 38 mounted on the output shaft of the rotation drive motor 34 which is mounted on the bed 50 and through an endless belt 37 which is disposed and put over the two pulleys 38 and 36.
On the other hand, as shown in FIG. 1 the pre-load applying member 70 comprises a pre-load slider 23 which is movable on the bed 50 along the axial direction of the spindle rotary shaft 1, while a nut 24a is fixedly secured to the pre-load slider 23. The nut 24a is brought in threaded engagement with a male screw 25 which is supported by a male screw support portion 26 mounted on the bed 50 in such a manner that the male screw 25 is rotatable around its own axis. The male screw 25 can be rotated by a pre-load drive motor 27. When the male screw 25 is rotated, the pre-load slider 23 is moved along the axial direction of the spindle rotary shaft 1. To the surface of the pre-load slider 23 that is opposed to the spindle rotary shaft 1, there is fixed one end 6a of a pre-load spring 6 serving as an elastic member, whereas a pre-load ring 22 is mounted on the other end 6b of the pre-load spring 6. The pre-load ring 22, due to the movement of the pre-load slider 23, is butted against the outer ring 4a of the ball bearing 4 to be inspected against the spring force of the pre-load spring 6, while a pre-load to be applied to the outer ring 4a of the ball bearing 4 to be inspected is determined in accordance with the moving position of the pre-load slider 23 and the spring constant of the pre-load spring 6.
When measuring vibrations generated from the ball bearing 4 to be inspected during the rotation of the ball bearing 4 to be inspected, that is, while the inner ring 4b is rotating relatively to the outer ring 4a, there is used a vibration measuring device consisting of a converter 40 or the like which is to be contacted directly with the outer ring 4a; and, the thus generated vibrations are converted into electrical signals by the converter 40, and the thus converted electrical signals are then input to a measuring device main body (not shown). The relative positioning between the converter 40 and outer ring 4a is achieved by adjusting the position of the converter 40 by a converter position adjust slider 41. Also, when measuring sound pressures generated from the ball bearing 4 to be inspected, there is used a sound pressure measuring device consisting of a microphone 42 or the like which is held at a predetermined interval from the ball bearing 4 to be inspected.
Next, description will be given below of an inspection procedure using the above-mentioned conventional inspection unit.
At first, the inner ring 4b of the ball bearing 4 to be inspected is mounted onto one end of the spindle rotary shaft 1. Next, the pre-load slider 23 is moved to a predetermined position to thereby cause the pre-load ring 22 to butt against the outer ring 4a of the ball bearing 4 to be inspected, so that a predetermined pre-load is applied to the outer ring 4a in the axial direction thereof.
Next, if the predetermined pre-load is applied to the outer ring 4a, then the spindle rotary shaft 1 is rotated by the rotation drive motor 34 and the inner ring 4b is thereby rotated with respect to the outer ring 4a. As shown in FIG. 2, as a result of such relative rotation of the inner ring 4b, due to the pre-load applied to the outer ring 4a, each of the steel balls 3 held between the respective grooves of the inner and outer rings 4b and 4a is in contact with the respective grooves of the inner and outer rings 4b and 4a at contact points A.sub.o and A.sub.i in such a manner that it forms a contact angle .alpha. with them. Namely, each of the steel ball 3 is rotated around about its own axis B, as an autorotation axis, intersecting at right angles to a straight line connecting its own contact points A.sub.o and A.sub.i and revolved around the axis of the spindle rotary shaft 1.
The vibrations or sound pressures that are generated from the ball bearing 4 to be inspected in the above-mentioned rotating condition are measured and, based on the measurement results, the ball bearing 4 to be inspected is inspected for its quality.
However, in the above-mentioned conventional inspection method, since each steel ball 3 is caused to rotate on the axis B as its rotation axis due to the pre-load applied to the outer ring 4a in such a manner that it forms the contact angle .alpha. with the respective grooves of the inner and outer rings 4b and 4a while it is in contact with them at the contact points A.sub.o and A.sub.i, the contact areas of the steel ball 3 with respect to the respective grooves of the inner and outer rings 4b and 4a are confined to the slight width areas each including therein a large circle corresponding to the equator with the axis B as a line connecting the south and north poles, with the result that there can be obtained only the measurement results covering several percent of surface area out of the whole surface area of each steel ball 3. Therefore, the finishing precision of the steel ball 3 and the presence or absence of damage on the surface of the steel ball 3 cannot be inspected over the whole area of the steel ball 3, that is, it is difficult to inspect the ball bearing 4 to be inspected with such a high inspection precision that can provide a sufficient guarantee for the quality of the ball bearing 4 to be inspected.